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Homework Help: Energy mass equivalence

  1. Jan 30, 2012 #1
    1. The problem statement, all variables and given/known data
    A particle has a mass of 4.032u. What is its mass in MeV/c2


    2. Relevant equations



    3. The attempt at a solution
    4.032u = 4.032 * 1.66*10-27 = 6.69*10-27 kg
    Energy equivalent, E = mc2: = (6.69*10-27)*(3*108)2 = 6.02 *10-10J

    J→eV (divide by 1.6∗10-19) )=3.76∗109 eV=3760 MeV

    How do I find it for MeV/c2
     
  2. jcsd
  3. Jan 30, 2012 #2
    1MeV/c^2 = 1e6*1.6e-19/9e16 kg = 1.7e-30 kg

    so 1 = [1MeV/c^2]/1.7e-30 kg = 1.7e-30 kg/[1MeV/c^2]

    multiply your answer, 6.69*10-27 kg, by the right factor above?
     
  4. Jan 31, 2012 #3

    vela

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    You tack on /c2 to the answer you found: 3760 MeV/c2.
     
  5. Jan 31, 2012 #4
    why is this true?
     
  6. Jan 31, 2012 #5

    vela

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    E = mc2 ⇒ m = E/c2 = (3760 MeV)/c2. You just don't actually plug in a value for c. Instead you make it part of the units.
     
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